1. Field of the Invention
This invention relates to a method for stabilizing a silver halide photographic material in the dry state.
2. Description of the Prior Art
Silver halide photographic materials in general are fixed by dissolving the silver halide using a fixation bath after the formation of an image, and then removing the dissolved silver complex ion by washing with water.
A method for stabilizing a silver halide photographic material intended for shortening the processing time is known. The method comprises converting the silver halide to a silver complex compound devoid of photosensitivity after the formation of an image, without performing a washing with water. Specifically, this method is performed by dipping a silver halide photographic material having an image formed thereon in an aqueous solution containing sodium thiosulfate, magnesium thiosulfate or thiourea as a stabilizer, and then drying the material (see Photographic Chemistry, Vol. 1, page 158, .zeta.149, Fountain Press, 1958). However, since this processing is a wet processing by which the photographic material is passed through an aqueous processing bath the photographic material must be dried in the final step. The presence of the drying step is a great defect from the viewpoint of shortening the treating time. Furthermore, the use of a treating liquid causes contamination of things around it or requires control with respect to the preparation or exchanging of the processing liquid. Accordingly, it would be very significant to provide a new dry stabilizing method.
Methods are known by which an image is formed on a silver halide photographic material using a dry treatment such as print out, thermo-development or photo-development in an attempt to remove the various defects of wet processing. However, in these methods also, the recorded images cannot be preserved unless they are stabilized, that is to say, unless the discoloration of the non-image area by light is prevented when the processed photographic material is allowed to stand in a bright room. In other words, a method of dry stabilization is required.
One of such dry stabilization methods is disclosed in U.S. Pat. Nos. 3,447,926 and 3,418,122. This method is one in which dry stabilization is carried out imagewise, and quite differs from the dry stabilization method in accordance with this invention. If stabilization is only carried out imagewise, the density of the image area changes progressively when the recorded photographic material stands in a bright place.
In contrast, the dry stabilization method of the present invention permits stabilization of both the image area and the non-image area simultaneously, and can lead to an inhibition of the light discoloration of the entire processed photographic material. Accordingly, the dry stabilization method of this invenion is complete in comparison with the dry stabilization described in the above-described U.S. Patents, and brings about the same effect in the dry state as the conventional wet stabilization method disclosed in the above-cited Photographic Chemistry.
Another conventional dry stabilization method is disclosed in U.S. Pat. NO. 3,615,510. This method comprises stabilizing the silver halide using a compound selected from the group consisting of organic sulfonium halides, organic sulfoxonium halides, organic ammonium halides, organic phosphonium halides, organic bronium halides, organic siliconium halides, and mixtures of these materials. According to the disclosure of this U.S. Patent, these compounds are complex salt-forming agents for the silver halide, and in order to make it possible to stabilize the silver halide by dry processing, an image stabilizing layer must be provided by adding such a compound to a low-melting non-aqueous solvent and a polymerizable binder in which the melted solvent can be diffused, and coating the mixture on the silver halide emulsion layer. When the photographic material so produced is heated, the solvent melts and the complex salt forming agent diffuses into the emulsion layer and reacts with the silver halide to thereby stabilize the photographic material.
In order to achieve this object, the manufacturing of the photographic material requires an additional step of providing the image-stabilizing layer adjacent the photographic layer. Furthermore, in order to diffuse the complex salt-forming agent into the emulsion layer entirely and stabilize the emulsion layer uniformly, it is necessary to add the complex salt-forming agent directly to the emulsion and thus to include a large amount of the complex salt forming agent in the image-stabilizing layer as compared with the amount required for stabilizing the emulsion layer. Alternatively, the complex salt-forming agent is coated on a developing web, and the photographic material is heated while in contact with it. These methods, however, require a complicated operating procedure.
Another procedure can be used in which an aqueous solution of a stabilizer is added to the emulsion at room temperature or at a lower temperature to include the stabilizer in the emulsion layer. However, if the stabilizer is included in the emulsion in an amount sufficient for stabilization, it greatly affects the photographic properties of the material.
The three procedures of using the stabilizer are undesirable for various reasons such as the increased number of manufacturing steps, the troublesome operations, and the great influence on the photographic properties. A preferred procedure which lends itself to the easiest operation involves adding a stabilizer to an emulsion in the molten state, that is, an emulsion heated to a temperature higher than room temperature, for example, to 40.degree.C. to disperse the stabilizer sufficiently uniformly in the emulsion, and then coating the dispersion on the support.
An object of this invention is to provide a method of dry stabilization of a silver halide photographic material.
Another object of this invention is to provide a method for dry stabilization of a silver halide photographic material using a stabilizer that can be directly added to an emulsion in the molten state.
Still another object of this invention is to provide a method for the dry stabilization of a silver halide photographic material using a stabilizer which does not require the use of a stabilization promotor such as a low-melting non-aqueous solvent.